Surgeons working in the field of spinal surgery make use in particular of systems that consist essentially of a plate in which an orifice and a slot are formed, and of screws each having a shank with a bone thread terminated by a shoulder head, such screws being suitable for cooperating with the plate so that plate bearing against the vertebrae is held captive between the vertebrae and the shoulder heads of the screws.
Those spinal osteosynthesis systems present drawbacks, in particular because the spinal processes make it difficult to place bone-thread screws in the orifices in the plate so they can be screwed into the vertebral bodies, and do not allow for easy adjustment of the distance between the two segments of vertebrae by the surgeon in order to eliminate the source of pain and bring the segment of the spinal column back to its normal height.
In an attempt to overcome those drawbacks, systems have been developed comprising pedicular screws, lugs, first means for fastening a first end of each lug onto the head of a pedicular screw, at least one plate, and second means for fastening the plate onto the other end of each lug. Nevertheless, those systems are still relatively complex in terms both of putting them in place and of achieving good adjustment to the various distances.